1. Field of the Invention
This invention relates to a method of manufacturing a capacitor of a semiconductor device. The present invention relates particularly to a method of annealing a Ta.sub.2 O.sub.5 film having a high relative dielectric constant, which is formed on a metal or metal oxide electrode.
2. Description of the Related Art
A relative dielectric constant of a Ta.sub.2 O.sub.5 film formed on polycrystal silicon ranges from 20 to 28. This relative dielectric constant is three times or more than that of a silicon nitride film. Therefore, the introduction of the Ta.sub.2 O.sub.5 film into a process has been studied with the Ta.sub.2 O.sub.5 film as a DRAM (Dynamic Random Access Memory) capacitor dielectric of 256 Mbit or later.
It has recently been reported and noted that a Ta.sub.2 O.sub.5 film formed on an electrode composed of a metal such as Pt, Ru or the like has indicated a relative dielectric constant close to 50.
A Ta.sub.2 O.sub.5 film immediately after its deposition, which has been formed by CVD (Chemical Vapor Deposition), produces a large leakage current. A problem on such a leakage current characteristic can be improved by post anneal subsequent to the above formation.
This point of view will be described in detail. Many impurities caused by a raw gas are contained in the Ta.sub.2 O.sub.5 film obtained immediately after its formation. Oxygen is also often deficient in the Ta.sub.2 O.sub.5 film. These impurities and oxygen deficiencies are considered to serve as current paths and thereby result in a large leakage current flow.
Therefore, the Ta.sub.2 O.sub.5 film is heat-treated at a high temperature near 800.degree. C. in an atmosphere of oxygen or at a comparatively low temperature of 400.degree. C. or less in an atmosphere of ozone or nitrogen oxide to reduce the impurities and oxygen deficiencies in the Ta.sub.2 O.sub.5 film, whereby the leakage current can be greatly reduced.
However, if the Ta.sub.2 O.sub.5 film deposited on the metal electrode is post-annealed at a temperature of 600.degree. C. or less, it is then kept in an amorphous state. Thus, the relative dielectric constant thereof results in about 25 similar to the value of a Ta.sub.2 O.sub.5 film on a silicon electrode and the leakage current is less than or equal to 10.sup.-8 (A/cm.sup.-2).
On the other hand, when the Ta.sub.2 O.sub.5 film on the metal electrode is heat-treated at a high temperature of 700.degree. C. or more, the Ta.sub.2 O.sub.5 film is crystallized so that its relative dielectric constant is increased to about 50. However, the leakage current is increased by one digit or more as compared with the Ta.sub.2 O.sub.5 film kept in the amorphous state.
Therefore, the implementation of the Ta.sub.2 O.sub.5 film on the metal electrode, which is indicative of the large relative dielectric constant of 50 or more, needs to decrease the leakage current in the crystallized Ta.sub.2 O.sub.5 film.